A driver assistance system is understood as a device in a motor vehicle which supports the driver in driving the vehicle. One example of such a driver assistance system is, for example, an adaptive cruise control system (ACC system). This system makes it possible to find the position of vehicles traveling ahead with the aid of a sensor, typically with the aid of a radar sensor, and to regulate the speed of the host vehicle as a function of the measured distance to the vehicle traveling ahead in such a way that the vehicle traveling ahead, hereinafter referred to as “vehicle ahead,” is followed at a reasonable safety distance.
Driver assistance systems are also understood as safety systems that warn the driver of danger and/or automatically intervene in the driving of the vehicle to avert the danger if possible or to limit the damage or activate passive safety systems such as airbags, seat belt tensioners and the like to mitigate the consequences of an accident. Systems of this type are known, for example, as pre-crash systems or PSS systems (predictive safety systems).
In general, a driver assistance system includes a sensor component for detecting the surrounding traffic, including at least one sensor, a radar sensor for example, and corresponding electronic devices for data preparation, an actuator component, which intervenes in the drive system, the brake system, or the steering of the vehicle, and/or a driver interface for outputting warning signals to the driver, as well as a data processing device, which generates control signals for the actuator component on the basis of the data provided by the sensor component.
The function of the data processing device depends, at least implicitly, on one or more environmental hypotheses which determine how the sensor data are interpreted. For example, an environmental hypothesis for the ACC assistance function may be the following: “There is a vehicle ahead, which has distance d and relative velocity v with respect to the host vehicle.” Since the data delivered by the sensor device, for example, the radar sensor, are continuously updated in successive measuring cycles, environmental hypotheses could additionally contain the following statement: “The vehicle ahead detected in the current cycle is identical to the vehicle ahead which was positioned in the previous measuring cycle.”
If a driver assistance system has a plurality of assistance functions, e.g., a combination of ACC and PSS, it is desirable for the sensor component needed for the ACC function, i.e., the radar sensor for example, and if possible also the corresponding data preparation system, to also be used for the PSS function to reduce the overall installation complexity required.
However, this concept encounters a limitation in the data preparation stage, at the latest, since the measuring data for the different assistance functions must be prepared in different and specific ways adapted to the particular function. Accordingly, the underlying environmental hypotheses are also specifically adapted to the assistance function. For example, an environmental hypothesis for the PCC function may be the following: “There is an obstacle whose distance is at least dmin and whose (usually negative) relative velocity is at least vmin.” While the output quantities distance and relative velocity, which are transferred to the ACC function and the PSS function, are formally the same, their meanings and specific numerical values are not identical. While for distance regulation within the ACC function it is sufficient to know the most probable values of the distance and relative velocity, in a safety function such as PSS, the tolerance limits or the probability distributions of these quantities are also relevant. In particular, in a safety function, the most probable value of the distance is less relevant than the still remaining distance of the obstacle from the host vehicle assuming the most unfavorable case and taking into consideration all measuring inaccuracies.
This is also true for other quantities calculated from the raw data delivered by the radar sensor. For example, in the case of an angle-resolving radar sensor, it is possible to calculate transverse position y of an object relative to the longitudinal axis of the host vehicle from the measured azimuth angle of the object and its distance. In the case of a vehicle ahead within the ACC function, this quantity is relevant for the decision of whether the vehicle is in its own lane or on a neighboring lane. The term “vehicle ahead” includes the notion that the vehicle is traveling on the same lane as the host vehicle. In contrast, in the case of the PSS function, obstacles which only partially protrude into the host vehicle's lane or approach the host vehicle's lane from the side are also taken into account. In addition, in this case it would be relevant to ask whether it is possible to drive around the obstacle. In this context, additional information about the possible width of the object would also be desirable. Such information may be obtained in principle from the radar data if there is a plurality of reflection centers in the case of a very wide object such as a truck so that radar echoes, for which the distances and relative velocities are identical, but the azimuth angles are slightly different, are obtained. In contrast, this width information is not needed for distance regulation within the ACC function.
These examples illustrate that, although the different assistance functions depend on partially identical measuring quantities, they each require specific preparation of these measured quantities.
The underlying terms of the environmental hypotheses “vehicle ahead” and “obstacle” are also not identical, since their definitions depend on the different criteria and boundary conditions. For example, the environmental hypothesis “vehicle ahead” may assume that the ACC system is active and is in the follow mode. Since ACC systems are typically activatable only when the velocity of the host vehicle is above a certain minimum value, this also implies certain conditions regarding the velocity of the host vehicle. The term “vehicle ahead” typically also implies that the driver of this vehicle is traveling in a comfort-oriented mode, i.e., he will foreseeably not perform any abrupt maneuvers such as full braking or the like. Although there may be similar boundary conditions for the environmental hypothesis “obstacle,” they are not identical to those for a vehicle ahead. For example, a vehicle traveling ahead which performs sudden emergency braking qualifies as an obstacle, and no longer as a vehicle ahead.
For the ACC systems in use today, the term “vehicle ahead” also implies a moving object. In contrast, the environmental hypothesis “obstacle” within a PSS function should also refer to stationary objects whenever possible. In a variant of the ACC function known as “stop-and-go” it again behaves differently and, when approaching a traffic jam, it allows the host vehicle to be braked to a standstill when the vehicle ahead stops. In this case the definition of the term “vehicle ahead” will also include stationary objects, as long as these objects have moved at some time in the past.
Due to the different term definitions on which the different environmental hypotheses are based, and due to the different nature of the output data for the different assistance functions, it has also been possible to use the raw data of a shared sensor, although further preparation of the data must take place in specially adapted processing stages.